In a new draft heritage management plan for the war memorial compiled by GML Heritage and recently released for comment, Anzac Hall - which sits behind the main war memorial building - was described as "architecturally impressive".

The firm recommended the hall's "important architectural qualities" be "respected" and any future change be " sympathetic to the heritage values" of the war memorial.

It also said the siting and architectural form of the hall had a "medium tolerance for change", meaning its "architectural form/design, location and use of the place embody the heritage significance of the component and its contribution to the Australian War Memorial".

"The component should be retained and conserved. However, it may be altered to some degree without adverse impact on heritage significance," the plan said.

However the hall, which was completed in 2001 at a cost of about $17 million and houses some of the memorial's prized artefacts such as the Lancaster bomber G for George, is likely to be knocked down next year as part of the war memorial's expansion.

The decision prompted outcry last year from the firm that designed the hall.

Denton Corker Marshall director John Denton said at the time: "Anzac Hall was the most important building we did there ... it was also the toughest achievement".

The heritage management plan praises the design of Anzac Hall for the way it sits "comfortably" next to the original war memorial building.

"With battered walls and a curved turret roof design, the structure evokes a battleship," the plan said.

But a spokesman for the war memorial said the heritage plan was separate to the redevelopment, and was "guidance" to help meet the requirements under law for managing the overall heritage values of the site.

He said the plan was a "complex and nuanced document", which did not prevent any changes on the site, including Anzac Hall, but required the memorial to "strongly consider" any impact on heritage actions may have.

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He also said the expansion project was "subject to the same government processes as any other project", which would require a heritage impact assessment to be provided to the government for consideration as part of its referral under the Environment Protection and Biodiversity Conservation Act.

"In order not to prejudice this process the memorial is not able to discuss specific matters that will be part of the heritage impact assessment at this time," the spokesman said.

Outgoing war memorial director Brendan Nelson said the design of the hall left them with few options.

"The architects at the time produced three designs, two allowed for future extension, they were modular designs and one did not allow for any future extension ad that was the design that was chosen," Dr Nelson said.

"As the architects said to us in the process of the detailed business case, the least complex and best value for money approach to redevelopment in the rear of the building is the removal of Anzac Hall.

"What makes Anzac Hall important is not the building, it's what's in it, it's the stories of the men and women in the artifacts that are so magnificently displayed by our staff and so I'm very confident we made the right decision."

The expansion bid includes plans to rebuild Anzac Hall over three levels, increasing exhibition space and creating a new entrance and research area.

The lower floor of the war memorial will be completely redesigned, a new underground exhibition hall built to display helicopters and jet fighters but the original facade of the building will be retained.

The heritage plan comes after the war memorial walked back from plans to turn a remembrance park into a temporary car park for contractors during the expansion.

Have your say on the draft heritage management plan until September 4.